Image caption
Batman: The Dark Knight, starring the late Heath Ledger as The Joker, is the second most pirated film

US net firm Verizon has declared war on illegal downloaders, or pirates, who use technologies such as BitTorrent to steal copyrighted material.

Verizon has said it will first warn repeat offenders by email and voicemail.

Then it will restrict or "throttle" their internet connection speeds.

Time Warner Cable, another US internet service provider (ISP) pledging to tackle piracy, says it will use pop-up warnings to deter repeat offenders.

Private enforcers

After that it will restrict subscribers' web browsing activities by redirecting them to a landing page.

The moves come as part of a concerted effort by five major US ISPs - AT&T, Cablevision, Comcast, Time Warner Cable and Verizon - to bear down on illegal downloading and sharing of copyrighted material.

In September 2011, the Motion Picture Association of America (MPAA) and the Recording Industry Association of America (RIAA) teamed up with the ISPs to launch the Center for Copyright Information, a body dedicated to deterring copyright infringement and advising consumers on legal file sharing options.

Verizon and Time Warner unveiled their latest anti-piracy plans at a panel discussion hosted by the Internet Society in New York on Thursday.

Top 10 most pirated films

1. Avatar

2. Batman: The Dark Knight

3. Transformers

4. Inception

5. The Hangover

6. Star Trek

7. Kick-Ass

8. The Departed

9. The Incredible Hulk

10. Pirates of the Caribbean: At World's End

Source: TorrentFreak

Dubbed the "six-strikes" policy, referring to the number of warnings pirates may receive, the campaign is due to kick off in full from the end of November, according to file-sharing news site TorrentFreak.

But the industry freely admits that the campaign is unlikely to deter "hardcore" pirates, who can easily circumvent the copyright alert system by setting up virtual private networks.

It claims the campaign is aimed at educating mainstream consumers who may not even realise they are doing something illegal.

While the industry maintains it has no plans to take legal action against persistent offenders, observers believe it remains the ultimate sanction.

The Electronic Frontier Foundation, which campaigns for digital freedom, is highly critical of the imminent campaign, saying: "Big media companies are launching a massive peer-to-peer surveillance scheme to snoop on subscribers."

ISPs will be acting as "Hollywood's private enforcement arm", it added.